Question: Luis is 36 years old and William is 6 years old. How many years will it take until Luis is only 3 times as old as William?
Solution: We can use the given information to write down an equation about how many years it will take. Let $y$ be the number of years that it will take. In $y$ years, Luis will be $36 + y$ years old and William will be $6 + y$ years old. At that time, Luis will be 3 times as old as William. Writing this information as an equation, we get: $36 + y = 3 (6 + y)$ Simplifying the right side of this equation, we get: $36 + y = 18 + 3 y$ Solving for $y$ , we get: $2 y = 18$ $y = 9$.